Magnetic tripping mechanism for thermal circuit breaker

ABSTRACT

A CIRCUIT BREAKER HAVING A THERMAL BIMETAL OPERATING MEMBER WITH AN INDEPENDENT MAGNETIC TRIP ACTUATING MECHANISM. THE BIMETAL TRIP MEMBER IS IN CIRCUIT WITH THE CURRENT FLOW THROUGH THE CIRCUIT BREAKER AND ON HEATING PIVOTS IN A DIRECTION TO TRIP THE CIRCUIT BREAKER. A PLASTIC ARMATURE IS PIVOTALLY MOUNTED ADJACENT THE BREAKER LEADS ON ONE SIDE OF THE BREAKER AND IS PROVIDED WITH MAGNETIC   INSERTS. A PUSH ROD IS PROVIDED CONNECTED BETWEEN THE PLASTIC ARMATURE AND THE BREAKER LATCH MECHANISM. ON SEVERE FAULT CURRENTS THE CURRENT FLOW THROUGH THE BREAKER LEADS ATTRACTS THE MAGNETIC INSERTS PIVOTING THE PLASTIC ARMATURE IN A DIRECTION TO TRIP THE CIRCUIT BREAKER.

Dec 12, 1972 P. J. HOPKINSON MAGNETIC TRIPPING MECHANISM FOR THERMAL CIRCUIT BREAKER Filed Sept. 22, 1970 2 Sheets-Sheet 1 Dec; 12, 1972 P. J. HOPKINSON 3,706,058

MAGNETIC TRIPPING MECHANISM FOR THERMAL CIRCUIT BREAKER Filed Sept. 22, 1970 2 Sheets-Sheet Z United States Patent O US. Cl. 335-174 8 Claims ABSTRACT OF THE DISCLOSURE A circuit breaker having a thermal bimetal operating member with an independent magnetic trip actuating mechanism. The bimetal trip member is in circuit with the current flow through the circuit breaker and on heating pivots in a direction to trip the circuit breaker. A plastic armature is pivotally mounted adjacent the breaker leads on one side of the breaker and is provided with magnetic inserts. A push rod is provided connected between the plastic armature and the breaker latch mechanism. On severe fault currents the current flow through the breaker leads attracts the magnetic inserts pivoting the plastic armature in a direction to trip the circuit breaker.

BACKGROUND OF THE INVENTION This invention relates to circuit breakers and more particularly to a separate magnetic tripping mechanism which may be added to a thermal circuit breaker.

Thermal and magnetic circuit breakers for electrical apparatus are well known in the art. In these circuit breakers the thermal portion includes a bimetal element through which the current of the electrical apparatus flows. As overcurrent conditions are experienced, the bimetal member becomes heated causing it to bend in a direction to unlatch or open the contacts of the circuit breaker. As the circuit breaker opens it removes the electrical power to the protected apparatus, as is well understood. Magnetic tripping devices have been provided in such breakers to trip the circuit breaker rapidly in the event of excessive overload of current which would rapidly damage the electrical apparatus being protected. As is well known, bimetal members require a substantial period to become heated sufiiciently to actuate the trip mechanism regardless of the amount of overcurrent flowing. However, on excessive overcurrents, that is, substantially over the rated load current of the apparatus, it is general- 1y desired to trip the circuit breaker rapidly and remove the overcurrent condition from the apparatus. When a magnetic trip is provided, it is attracted by the magnetic flux generated by the overcurrent condition thereby causing the breaker to trip open.

Most present day circuit breakers provide a magnetic trip member which is mounted adjacent the thermal or bimetal member and is actuated by the flux in the thermal member. While this has proved very successful in many designs, it has led to difiiculty in including a magnetic trip in many types of circuit breakers without completely redesigning such circuit breakers. Also, most present day magnetic trip members utilize a pivoted steel member as a magnetic armature for the magnetic trip mechanism. These armatures represent substantial mass or inertia and have led to some difliculty in accurately calibrating the magnetic trip for the desired excess overcurrent pickup. This has limited most designs of circuit breakers having magnetic trip mechanisms to one or two ratings, since a steel armature of a given mass is only usable within a range of one or two ratings. It has been considered desirable to develop a magnetic trip mechanism which could be used with many types of circuit breakers without requiring a basic redesign of such circuit breakers. Further, it is considered desirable to provide a magnetic trip mechanism which may be readily incorporated into circuit breakers and which may be readily calibrated for a variety of electrical apparatus without the necessity of utilizing separate magnetic armatures, according to the rating of such appaartus.

It is, therefore, a principal object of this invention to provide a magnetic trip mechanism for use in a thermal circuit breaker.

A further object of this invention is to provide a light weight magnetic trip mechanism for a circuit breaker which may be readily calibrated for a variety of ratings or overcurrent conditions.

A still further object of this invention is to provide a magnetic trip mechanism for use in thermal circuit breakers which may be readily incorporated into such circuit breakers without the necessity of a major redesign of such circuit breakers.

SUMMARY OF THE INVENTION Briefly, in one form, this invention comprises a pivotal plastic armature having magnetic inserts as a magnetic trip mechanism for a circuit breaker. The plastic armature is mounted on pivots adjacent to a set of the current carrying leads of the circuit breaker. A push rod is provided between the armature and the circuit breaker latch mechanism for tripping the circuit breaker on overload currents. A spring member is provided holding the armature in non-trip position, the spring providing a current pickup calibration means.

The invention which is sought to be protected will be particularly pointed out and distinctly claimed in the claims appended hereto. However, it is believed that this invention and the manner in which its various objects and advantages are obtained, as well as other objects and advantages thereof, will be better understood by reference to the following detailed description of a preferred embodiment thereof, particularly when considered in the light ofthe accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a perspective view, with parts broken away, of a thermal circuit breaker having a preferred form of magnetic trip mechanism included therein, according to this invention;

FIG. 2 is a sectional side view of the circuit breaker of FIG. 1 showing the magnetic trip mechanism of this invention in greater detail;

FIG. 3 is a partial, perspective view of the preferred form of magnetic trip mechanism according to this invention; and

FIG. 3A is a perspective view of a preferred form of magnetic insert.

DESCRIPTION OF THE PREFERRED EMBODIMENT As is well known to those skilled in this art, circuit breakers are provided in electrical apparatus to protect such apparatus from overcurrent conditions. The circuit breaker is usually mounted in the electrical apparatus, which may be filled with a dielectric fluid, such as an oil filled distribution transformer. The circuit breakers are usually provided with a thermally actuated trip mechanism such that the circuit breaker will open when the electrical apparatus is subjected to overcurrent conditions. However, under severe overcurrent conditions, it is generally desired to open the circuit breaker much more rapidly than can be done with a thermally actuated device. This may be done in many circuit breakers by the use of a magnetic trip mechanism in the circuit breaker. According to this invention, a pivoted magnetic trip device is provided that may be readily added to a thermal circuit breaker. For an understanding of the invention, reference will now be made to the drawings for a detailed description of the preferred embodiment. Like numerals will be used to indicate like parts throughout the various views.

FIGS. 1 and 2 show a thermally actuated circuit breaker to which has been added the preferred form of magnetic trip device of this invention. As shown, a two-pole circuit breaker 10. Each pole of circuit breaker also has a on one side of circuit breaker 10 and with another terminal 14, for each pole, on the other side of the circuit breaker 10. Each pole of circuit breaker 10 also has a fixed contact 16, which is electrically connected to the terminal 12, and a movable contact 18, which is electrically connected to terminal 14. The movable contact 18 of each pole is connected to an actuating shaft 20, which serves to open and close the contacts 18 with the fixed contacts 16 in a known manner. Shaft 20 is actuated through a known mechanical tripping mechanism 22 (not shown in detail). As is well understood, when tripped the mechanical mechanism 22 causes the movable contacts 18 to separate from the fixed contacts 16 with a rapid snap action. The mechanism 22 must be manually reset to move contacts 18 back into engagement with the contacts 16.

In the form shown in FIGS. 1 and 2, terminal 12 is connected to contact 16 through a lead 24. and bimetal thermal member 26. The bimetal 26 is fixed to the contact 16 and to circuit breaker 10 by means of bolt 28 which secures one end 30 of the bimetal 26. In the preferred embodiment shown, insulation member 31 is provided to insulate lead 24 from the fixed end 30 of bimetal 26. The opposite end 32 of bimetal 26 is free and is connected electrically to lead 24. End 32 has secured thereto an extension 34 which contacts a triggering plate 36 which pivots about a bar or pin 38. As is well understood, when current flows in circuit breaker 10 it flows through terminal 12, the lead 24, bimetal 26, contacts 16 and 18, through flexible lead 40 and through the terminal 14.

I When overcurrent flows through the circuit breaker 10,

such overcurrent causes bimetal 26 to heat up. As the heat increases, bimetal 26 bends clockwise (as seen in FIGS. 1 and 2) about the fixed end 30. If the overcurrent condition is suflicient and continues long enough, it will cause the extension 34 to contact pivot plate 36 pivoting such plate about pin 38 and tripping the mechanism 22 to open the contacts 16, 18 in a well known manner, as is shown in FIG. 1.

!In order to provide for rapid opening of the contacts 16, 18 when excessive overcurrent flows in the circuit breaker 10, a novel magnetic trip device 50 is provided. The magnetic trip mechanism 50 includes a plastic armature 52 which is pivotally mounted in the side walls 42, 44 of the circuit breaker 10 (only a portion of wall 44 being shown, see FIG. 1). As shown in FIG. 1, plastic armature 52 has pivot members 54. formed at each end thereof. The pivot members 54 fit into openings 46, 48 in the walls 42, 44, respectively, which act as bearing for pivot members 54 and the armature 52. An

. extension 56 is provided on armature 52, such extension 56 carrying a push'rocl 58 which contacts trigger plate 36 by means of the curved end 60. A restraining spring 62 is provided, one end being connected to rod 58 at 64 While the other end is connected to bracket 66 on wall 42 (see FIG. 3). 7

As best shown in FIG. 3, plastic armature 52 is provided with a magnetic insert 68 adjacent each lead or is formed of a plurality of laminations of steel to provide better flux distribution through insert 68 and better flux coupling between the lead 14 and insert 68. Restraining spring 62 holds the push rod 58 in an upward position which holds armature 52 pivoted clockwise (as seen in FIG. 3) about pivots 54 and away from the leads 14, despite normal current flow in leads 14. As excess current flows in leads 14, the flux generated by such current attracts the inserts 68, overcomes restraining spring 62 and pivots armature 52 counterclockwise about pivot members 54. As armature 52 pivots counterclockwise, it forces rod 58 downward against the trigger plate 36. This will pi'vot trigger plate 36, tripping mechanism 22 and opening contacts 16, 18. As will be understood, the excess current necessary to attract armature 52 can be accurately set by means of restraining spring 62. If it is desired to open contacts 16, 18 on a relatively low overload current, a weak spring 62 will be provided. If it is desired to open contacts 16, 18 only on a high overload current, a relatively strong spring 62 would be used.

From the above description, it will be clear that a novel magnetic trip mechanism 50 has been provided which may be readily added to thermal circuit breakers. As will be understood, the magnetic trip 50 may be attached to a circuit breaker having any number of poles, it only being necessary to provide a magnetic insert 68 to the armature 52 adjacent to one lead from each pole.

While there has been shown and described the present preferred embodiment of this invention, it will be obvious to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention, particularly as it is set forth in the appended claims.

What is claimed as new and which it is desired to secure by Letters Patent of the United States is:

1. A circuit breaker including a set of leads into and a set of leads out of said circuit breaker, an incoming lead and an outgoing lead being provided for each pole, a pair of contacts inserted between said incoming and outgoing lead for each pole, one contact of said pair of contacts for each pole being movable into and out of electrical connection with the other of said pair of contacts, a mechanical trip mechanism for opening said contacts, a thermal element inserted between said incoming and outgoing leads, said thermal element acting on said mechanical trip mechanism to open said contacts on overcurrent conditions; and a magnetic trip mechanism for said circuit breaker, said magnetic trip mechanism comprising a plastic armature pivotally mounted in said circuit breaker adjacent one of said sets of leads, a magnetic insert in said' armature opposite each lead of said adjacent set of leads, a push rod connected between said armature and said mechanical trip mechanism, a restraining spring between said trip rod and a wall of said circuit breaker holding said armature away from said adjacent set of leads, said armature adapted to be attracted to said adjacent set of leads by flux generated by excessive overcurrent fiow in said adjacent set of leads causing said push rod to actuate said mechanical trip mechanism.

2. A circuit breaker as claimed in claim 1 in which said magnetic insert includes a plurality of steel laminations.

3. A circuit breaker including a set of leads into and a set of leads out of said circuit breaker, an incoming lead and an outgoing lead being provided for each pole, a pair of contacts inserted between said incoming and outgoing lead for each pole, one contact of said pair of contacts for each pole being movable into and out of electrical connection with the other of said pair of contacts, a mechanical trip mechanism for opening said contacts, a thermal element inserted between said incoming and outgoing leads, said thermal element acting on said mechanical trip mechanism to open said contacts on overcurrent conditions; and a magnetic trip mechanism for said circuit breaker, said magnetic trip mechanism comprising a plastic armature pivotally mounted in said circuit breaker adjacent one of said sets of leads, a magnetic insert in said armature opposite each lead of said adjacent set of leads, a push rod connected between said armature and said mechanical trip mechanism, a restraining spring between said magnetic trip mechanism and a Wall of said circuit breaker holding said armature away from said adjacent set of leads, said armature being attracted to said adjacent set of leads by flux generated by excessive overcurrent flow in said circuit breaker causing said push rod to actuate said mechanical trip mechanism.

4. A circuit breaker as claimed in claim 3 in which said magnetic insert includes a plurality of steel laminations.

5. A magnetic trip mechanism for use in a circuit breaker, said magnetic trip mechanism comprising:

a plastic armature, means on said plastic armature for pivotally mounting said plastic armature in a circuit breaker adjacent a set of leads,

a magnetic insert mounted in said plastic armature for each pole of the circuit breaker, connecting means attached to said plastic armature for engaging the mechanical trip mechanism of a circuit breaker and restraining means connected to said magnetic trip mechanism for holding said plastic armature and said connecting means in an inactive position.

6. A magnetic trip mechanism as claimed in claim 5 in which said magnetic insert includes a plurality of steel laminations.

7. A circuit breaker including a set of leads into and a set of leads out of said circuit breaker, an incoming lead and an outgoing lead being provided for each pole, a pair of contacts inserted between said incoming and outgoing leads for each pole, one contact of said pair of contacts for each pole being movable into and out of electrical connection with the other of said pair of contacts, a mechanical trip mechanism for opening said contacts, a thermal element inserted between said incoming and outgoing leads, said thermal element acting on said mechanical trip mechanism too pen said contacts on overcurrent conditions; and a magnetic trip mechanism for said circuit breaker, said trip mechanism comprising a plastic armature pivotally mounted in said circuit breaker adjacent one of said sets of leads, a magnetic insert in said armature opposite each lead of said adjacent set of leads, connecting means connected between said armature and said mechanical trip mechanism, restraining means between said magnetic trip mechanism and a fixed position of said circuit breaker holding said armature away from said adjacent set of leads, said armature being attracted to said adjacent set of leads by flux generated by excessive overcurrent flow in said adjacent set of leads causing said connecting means to actuate said mechanical trip mechanism when said generated flux is sufficient to overcome said restraining means.

8. A circuit breaker as claimed in claim 7 in which said magnetic inserts comprise a plurality of steel laminations.

References Cited UNITED STATES PATENTS 3,277,407 10/ 1966 Kobayasi 335- 3,128,355 4/1964 Fuller 335-203 2,412,304 12/ 1946 Staley 335-279 3,163,805 12/1964 Vash et a1 335-276 HAROLD BROOME, Primary Examiner US. Cl. X.R. 335-203, 279

"UNETQZE STATES *4 Patent No. 397 9 5 Dated DECEMBER 12, 1972 Inventor) PM L 1 P J. How I NSON It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Cu. 3, L NES 10 TO 13 CANCEL TO ON L 1 NE 13,

AND INSERT :s PROVlDED WITH A TERMtNAL 12, FOR EACH POLE, ON ONE SIDE OF CIRCLHT BREAKER 10 AND WITH ANOTHER TERMlNAL 1 FOR EACH PoLE,

ON THE OTHER snot of THE CIRCUIT BREAKER 10.

CoL. 6, LINE 5, "Too PEN" SHOULD READ TO OPEN Signed and sealed this ZEltE day of May- 1973 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents Patent No. 397 9 5 Dated DEcENBER 12, 1972 Inventor) PHI L l P J. HOPK I NSON It is certified that error appears iri the above-identified patent and that said Letters Patent are hereby corrected as shown below:

COL, 3, LINES 10 TO 13 cANcEL TO ON L|NE 13,

AND :NsERT IS PRovioEO WITH A TERMlNAL 12, FOR EACH POLE, ON ONE SIDE OE CIRCLHT BREAKER 10 AND WITH ANOTHER TERMlNAL 1 FOR EACH POLE,

ON THE OTHER snot OF THE ICIRCQUIT BREAKER 10.

COL. 6, LINE 5, "Too PEN" SHOULD READ TO OPEN Signed and sealed 29x5 da 0;? May 1973 (SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer v Commissioner of Patents 

